Stereophonic broadcasting receiving system with acoustic matrixing

ABSTRACT

A stereophonic sound reproducing system which finds particular application in an FM radio broadcasting receiver. The FM signal is demodulated and there is detracted therefrom a sum signal of the right and left stereo channels and a difference signal of the difference between the right and left stereo channels. The sum signal and a phase reversed sum signal are applied respectively to first and third loudspeakers. The difference signal is applied to a second loudspeaker which is positioned between the first and third speakers. By this arrangement stereophonic sound is produced without requiring a matrix circuit in the radio receiver. Furthermore, a stereophonic effect is perceived by the listener, and which effect is not particular dependent on the relative location of the speakers and the listener, nor on the acoustical properties of the room in which the sound is being reproduced.

United States Patent [191 Horigome [54] STEREOPHONIC BROADCASTING RECEIVING SYSTEM WITH ACOUSTIC MATRIXING [75] Inventor: Sunobu Horigome, Shinagawa-ku,

Tokyo, Japan [73] Assignee: Sony Corporation, Tokyo, Japan [22] Filed: Oct. 16, 1970 [21] Appl. No.: 81,438

[30] Foreign Application Priority Data Oct. 16, 1969 Japan ..44/82796 [52] US. Cl. ......179/l5 BT, 179/1 G [51] Int. Cl. ..H04h 5/00 [58] 'Field of Search ..179/15 ET, 1 G

[56] References Cited UNITED STATES PATENTS 3,310,632 3/1967 Snead ..l79/l5 BT 1 June 5, 1973 Primary Examiner-Kathleen H. Claffy Assistant Examiner-Thomas DAmico Attorney-Lewis H. Eslinger, Alvin Sinderbrand and Curtis, Morris & Safford [57 ABSTRACT A stereophonic sound reproducing system which finds particular application in an FM radio broadcasting receiver. The PM signal is demodulated and there is detracted therefrom a sum signal of the right and left stereo channels and a difference signal of the difference between the right and left stereo channels. The sum signal and a phase reversed sum signal are applied respectively to first and third loudspeakers. The difference signal is appliedto a second loudspeaker which is positioned between the first and third speakers. By this arrangement stereophonic sound is produced without requiring a matrix circuit in the radio receiver. Furthermore, a stereophonic effect is perceived by the listener, and which effect is not particular dependent on the relative location of the speakers and the listener, nor on the acoustical properties of the room in which the sound is being reproduced.

4 Claims, 3 Drawing Figures PATENIEDJUH 5 I973 SHEET 2 BF 2 INVENTOR. SUNUBU HOITI60ME STEREOPHONIC BROADCASTING RECEIVING SYSTEM WITH ACOUSTIC MATRIXING This invention relates to stereophonic receiving and reproducing systems.

A particular application of the invention is in home entertainment FM stereo radios. In the standard frequency modulation stereo broadcast system employed in the United States, a main carrier signal is frequency modulated by a composite signal. This composite signal has a frequency band width of approximately 67 KHz and is made up of three components. The first part of the composite signal .is a sum signal (L+R) which is the sum of the left channel stereo and the right channel stereo signals. The sum signal occupies the lower portion of the 67 KHZ frequency band of the composite signal and has a band width of approximately KHz. The second signal is asub-channel signal with a frequency range of approximately 23 to 53 KHz. The sub-channel signal is made up of a difference signal (i.e. the difference between the left stereo channel signal and the right stereo channel signal L-R), which is suppressed amplitude modulated on a 38 KHz sub-carrier. The third component is a pilot signal of 19 KHz, which is used in the receiver for demodulating the difference signal from the sub-channel signal. In a typical FM stereo receiver the incoming frequency modulated stereo signal is demodulated to produce the composite signal, which is divided into its three components: pilot, subchannel and sum signals. The pilot signal of 19 KHz is frequency doubled and then combined with the subchannel signal, which is demodulated to produce the difference signal (L-R). The sum and difference signals are then applied to a matrix circuit which separates the left channel signal and the right channel signal. The separate right and left channel signals are then applied to separate amplifiers and to independent speakers, wherein the sound is reproduced for presentation to listeners.

In the prior art system, the matrix circuit presents a number of undesirable features. One of them is that it is a fairly complicated circuit, and thus is expensive to manufacture, and expensive to tune. It also may require frequent repair. To avoid the shortcomings of the prior art system using a matrix circuit, this application provides a new system for stereophonic frequency modulated broadcast reproduction which does away with the need for the matrix circuit.

The sound reproduced in a system constructed in accordance with the invention is not noticeably different than the sound produced in the conventional stereo system having a matrix circuit. In fact, the sound reproduced in this system may under certain circumstances, be better than the sound produced with a conventional stereo receiver and reproducing circuit.

In the prior art systems, a left stereo signal and a right stereo signal are applied to separate loudspeakers. For proper sound reproduction, the speakers must be carefully positioned and the listener must be situated further from the loudspeakers than the distance between any two of the speakers. In small rooms, moreover, it is impossible for the two speaker system to faithfully reproduce stereophonic sound since the speakers must also be spaced apart from each other by some distance to give a satisfactory stereo effect. Ideally, for true reproduction, the size of the room in which the sound is reproduced should be that of the room in which such music would normally be produced, i.e. in a theater or symphony hall. Thus, many home stereophonic systems cannot faithfully reproduce stereophonic music because the room in which the sound is reproduced does not have the proper acoustical dimensions. In' the system of this invention, the stereophonic effect is electroacoustically produced, and does not heavily depend upon the dimensions and acoustic quality of the environment in which the loudspeakers are located.

A further advantage of this invention is that the expansion of sound can be easily adjusted so that it is possible to give the listener a satisfactory stereophonic effect with an extremely simple device.

. It is an object of the present invention to provide a novel radio broadcast frequency modulated stereophonic reception system.

It is another object of the present invention to provide a novel frequency modulated stereophonic reception system which does not require a matrix circuit of the prior art.

It is another object of the present invention to provide a novel stereophonic sound reproduction system.

It-is still another object of the present invention to provide a novel stereophonic sound reproduction system which provides a stereophonic effect electroacoustically, and with reduced reliance on the location of loudspeakers, and the acoustical properties of the room in which the sound is reproduced.

According to the invention there is provided in a stereophonic broadcasting receiving system for receiving a signal which consists of a main carrier which is modulated in frequency by a sum signal of right and left stereo channels, a pilot signal, and a suppressed subcarrier amplitude modulated by a difference signal of the difference between the right and left stereo channels, said system having a frequency modulation tuner for demodulating the sum signal of the right and left stereo channels, demodulating means for providing the difference signal between the right and left stereo channels, a first electro-acoustic wave transducer, means for coupling one of the sum and difference signals to the first electro-acoustic wave transducer, the electroacoustic wave transducer emitting two acoustic waves opposite in phase, and means for coupling the other of said two signals to a second electro-acoustic wave transducer means.

According to the invention there is also provided in a sound reproducing system of the kind adapted to receive a sum signal of the right and left stereo channel signals, and the difference signal, equal to the difference between the right and left stereo channel signals; three electro-acoustic wave transducers; means for coupling one of said signals to two of said electroacoustic wave transducers but with the signals in opposite phase, and means for coupling the other of said signals to the third of said electro-acoustic wave transducer.

The construction of an illustrative embodiment as well as further objects and advantages thereof, will become apparent when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a block diagram showing a conventional frequency modulation stereophonic broadcasting receiver of the prior art.

FIG. 2 is a block diagram illustrating one embodiment of an FM stereophonic broadcasting receiver in accordance with the present invention.

FIG. 3 is a graph illustrating a frequency response characteristic curve of a band pass filter employed in the embodiment of FIG. 2.

Referring now to FIG. 1 there is shown in block form a conventional frequency modulation stereo radio broadcast receiver. An antenna 1 picks the signals from the air waves and carries the received signals to an FM tuner 2. The tuner is manually controlled to select the desired station or program. Tuner 2 frequency demodulates the received signal and separates the composite signal from the FM main carrier. The composite signal is applied in parallel to three filters, 3, 4, and 5. Filter 3 is a low pass filter with a band pass of approximately to 15 KHZ and separates the sum signal (L+R) from the composite signal. The filter 4 is a band pass filter having a pass band in the range of approximately 23 to .53 KHZ. Band pass filter 4 separates the sub-channel signal from the composite signal. The sub-channel signal is a suppressed amplitude modulation of the difference signal (L-R) on a 38 KHZ sub-carrier. The filter 5 is a band pass filter tuned to pass a 19 KHZ pilot signal.

The sub-channel signal from the band pass filter 4 is applied to a mixer circuit 6. A second input to the mixer circuit 6 comes from a frequency doubler 7 which has as its input the 19 KHZ pilot signal from the band pass filter 5. The frequency doubler 7 doubles the 19 KHZ pilot signal to provide a 38 KHZ sub-carrier which is combined in the mixer circuit 6 with the subchannel signal. The output therefrom is then applied to a detector 8 which separates the difference signal (L-R) from the signal coming from the mixer circuit.

The sum signal (L+R) and the difference signal (L-R) coming respectively from the low pass filter 3 and the detector circuit 8 are applied to a matrix circuit 9 which combines and separates the signals to provide on two conductors separate left and right signals L and R. These left and right signals L and R are individually amplified by amplifiers 10L and 10R respectively and then supplied to left and right speakers 11L and 11R for reproduction.

In summary, the prior art system demodulates the received FM signal and extracts a sum signal and a difference signal. These two signals are then fed to a matrix circuit where they are combined to produce a left stereo channel signal and a right stereo channel signal. A pair of loudspeakers, one for the left stereo signal and one for the right stereo signal, reproduce the stereo sound from the separate right and left signals. The loudspeakers 11R and 11L and a listener have to be suitably relatively positioned in a listening room to achieve optimum stereo fidelity. Furthermore, the size and acoustic properties of the room greatly influence the quality of the reproduced sound. With the receiver and reproducing system of this invention as described below; stereophonic sound can be reproduced without the stringent requirement on loudspeakers and listener position, and listening room size. Furthermore, the circuit is simpler in that it does not require the matrix circuit of the prior art.

Referring now to FIG. 2 there is shown one embodiment of a frequency modulation stereo receiver constructed in accordance with this invention. An antenna and an FM tuner 101, which are the same as the antennal and tuner 2 shown in the system of FIG. 1 separates the composite signal from the received modulated FM signal. A trap circuit 105 is connected to the tuner 101. This trap circuit 105 has a parallel resonant circuit consisting of a coil 102 and a capacitor 103 for rejecting an unwanted received SCA signal of 67 KHZ. The composite signal from the tuner 110 is supplied, through a trap circuit 105 to a difference signal demodulator 104, which separates the difference signal L-R from the composite signal. The output from the trap circuit 105 is fed through a coupling capacitor 106 to a base of a transistor 107. A pair of biasing resistors 108 and 109 are connected in series between a power source +B (not shown) and ground with their common point connected to the base of the transistor 107. A resonance circuit is provided between the source 8+ and the collector of transistor 107 for extracting the pilot signal (19 KHZ) from the composite signal. The resonance circuit 110 is of the parallel L-C kind having a capacitor 113 connected in parallel with a primary coil 112 of a transformer 111, and this is tuned to pass a signal of 19 KHZ. The 19 KHZ signal appears on a secondary winding 114 of the transformer 110 and is applied to a frequency doubler 115, which produces the required sub-carrier signal of 38 KHZ. This subcarrier signal is to be applied to a mixer demodulator for subsequent separation of the amplitude modulated difference signal in the sub-channel signal. The 38 KHZ sub-carrier signal appears on the output of the frequency doubler 115 on a primary winding 117 of coupling transformer 16.

In the emitter circuit of the transistor 107, connected between emitter and ground, there is a RC tuned circuit 123. This is shown as a resistor 118 connected be tween emitter and ground; resistor 118 is shunted by the series combination of capacitor 119 and 120; and resistor 120 is in turn shunted by the series combination of capacitor 121 and resistor 122. The output from this circuit is taken at the junction of capacitor 121 with resistor 122. This circuit in combination with the trap circuit 105 and the input impedances of the capacitor 106 and the transistor 107, constitute a band pass filter which provides at the output (junction of capacitor 121 and resistor 122) the sub-channel signal whose frequency band is in the range of 23 to 53 KHZ. The frequency pass characteristics of this band pass filter circuit is shown in FIG. 3. In FIG. 3 it is seen that this filter circuit attenuates signals much below 23 KHZ and those signals much above 53 KHZ.

The sub-channel signal output from the band pass filter is applied to a center tap on a secondary winding 124 of the transformer 116. The secondary winding 124 is connected at its outer ends in a detector circuit arrangement made up of a pair of diodes 125 and 126 connected in series and poled in the same direction across the windings 124. The center point of the two diodes is shunted to ground by the parallel combination of a resistor 127 and a capacitor 128. In this detector circuit, the input is the sub-channel carrier signal of 38 KHZ from the frequency doubler, and the sub-channel signal in the frequency range of 23 to 53 KHz applied to the center tap on transformer 124. The output from the circuit is taken at the common point of the two diodes 125 and 126, and is the difference signal (L-R). This L-R signal is shown in the drawing by an arrow leaving the block 104.

The sum signal (L+R) R) is derived from the composite signal coming from FM tuner 101, by passing the composite signal through a low pass filter 131 made up of resistor 129 and capacitor 130. The sum signal is shown in the drawing as emerging from thefilter 131 by an arrow having the legend L+R.

The difference and sum signals (L-R, and L+R) are respectively supplied to potentiometers 132 and 133 which are coupled in gang relation to each other. Outputs derived from the potentiometers 132 and 133 are respectively supplied to amplifiers 136 and 137 through fixed and movable contacts 134a, 135a, and 134b, l35b of switches 134 and 135. At this time, the sum signal (L+R) from the potentiometer 133 is supplied to the fixed contacts 1340 and 13Sc of the switches 134 and 135.

The output derived from the amplifier 136 is supplied to a side speaker 138 and, at the same time, one portion of the output is inverted in phase by a phase-inverting switch 139 and then supplied to a side speaker 140. The phase-inverting switch 139 is operated in a ganged relation to the switches 134 and 135. The output derived from the amplifier 137 is directly supplied to a central speaker 141. Therefore, with the circuit illustrated in the figure sounds corresponding to the signals (L-R), (L+R) and R-L) are respectively reproduced by the speakers 138, 141 and 140. By this arrangement, the acoustic sounds from the three speakers produces the desired stereophonic effect for a listener. Thus, sounds corresponding to the left and right signals 2L and 2R are respectively emitted on the left hand and right hand sides of the listener.

The potentiometers 132 and 133 are designed such that when adjusted, the output signal from one of them becomes larger, while the output signal of the other becomes smaller. Thus, the ratio of the outputs of the left and right hand speakers 138 and 140 to that of the central speaker 141 can be changed, and the expansion of a sound is adjustable regardless of the arrangements of the speakers such as the spacing therebetween and direction thereof.

The ganged switches 134, 135, and 139 are also mono-stereophonic change over switches. When these switches are changed over from the state shown in the FIG. 3, only the sum signal (L+R) is supplied to the amplifiers 136 and 137 and the output of the speaker 140 is reversed in phase, so that the sounds corresponding to the sum signal (L+R) are reproduced from all the speakers. That is, normal monaural sound is emit ted from the three speakers. Further, instead of manually changing over the switches, they may be automatically changed over by detecting the presence of the pilot signal of the stereo broadcasting radio wave with some suitable circuit means. 7

Thus, the receiver of this invention does not involve the matrix circuit such as used in the conventional FM stereophonic receiver illustrated in FIG. 1, and hence does not require a phase correction circuit.

Further, each of the first, second and third speakers 138, 141 and described above need not always be individually housed but may be a plural speaker.

Although an illustrative embodiment of this invention has been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to that precise embodiment, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention.

What is claimed is:

1. A stereophonic broadcasting receiving system for receiving a signal which consists of a main carrier which is modulated in frequency by a sum signal of right and left stereo channels, a pilot signal, and a suppressed sub-carrier amplitude modulated by a difference signal of the difference between the right and left stereo channels, said system comprising: a frequency modulation tuner for demodulating the sum signal of the right and left stereo channels; demodulating means for providing the difference signal between the right and left stereo channels; a first electro-acoustic wave transducer, means for coupling the sum signal to the first electro-acoustic wave transducer; a second electro-acoustic wave transducer; first switching means for selectively coupling said second electro-acoustic wave transducer to said tuner to reproduce said sum signal or to said demodulating means for reproducing said difference signal; a third electro-acoustic wave transducer, and second switching means for selectively connecting said third electro-acoustic wave transducer in parallel with said second electro-acoustic wave transducer and alternately in-phase or 'out-of-phase with said second electro-acoustic wave transducer.

2. A stereophonic broadcasting receiving system as claimed in claim 1 wherein said second and third electro-acoustic wave transducers are relatively placed on opposite sides of said first electro-acoustic wave transducer.

3. A stereophonic broadcasting receiving system as recited in claim 2 wherein said first and said second switching means are mechanically interconnected such that when said second electro-acoustic wave transducer is connected to said tuner said third electroacoustic wave transducer is connected in parallel but out of phase with said second electro-acoustic wave transducer and when said second electro-acoustic wave transducer is connected to said demodulating means said third electro-acoustic wave transducer is connected in parallel and in phase with said second electro-acoustic wave transducer.

4. A stereophonic broadcasting receiving system as claimed in claim 1 which includes means for changing the ratio of the amplitudes of the sum signal to the difference signal. 

1. A stereophonic broadcasting receiving system for receiving a signal which consists of a main carrier which is modulated in frequency by a sum signal of right and left stereo channels, a pilot signal, and a suppressed sub-carrier amplitude modulated by a difference signal of the difference between the right and left stereo channels, said system comprising: a frequency modulation tuner for demodulating the sum signal of the right and left stereo channels; demodulating means for providing the difference signal between the right and left stereo channels; a first electro-acoustic wave transducer, means for coupling the sum signal to the first electro-acoustic wave transducer; a second electro-acoustic wave transducer; first switching means for selectively coupling said second electro-acoustic wave transducer to said tuner to reproduce said sum signal or to said demodulating means for reproducing said difference signal; a third electro-acoustic wAve transducer, and second switching means for selectively connecting said third electro-acoustic wave transducer in parallel with said second electro-acoustic wave transducer and alternately in-phase or out-of-phase with said second electro-acoustic wave transducer.
 2. A stereophonic broadcasting receiving system as claimed in claim 1 wherein said second and third electro-acoustic wave transducers are relatively placed on opposite sides of said first electro-acoustic wave transducer.
 3. A stereophonic broadcasting receiving system as recited in claim 2 wherein said first and said second switching means are mechanically interconnected such that when said second electro-acoustic wave transducer is connected to said tuner said third electro-acoustic wave transducer is connected in parallel but 180* out of phase with said second electro-acoustic wave transducer and when said second electro-acoustic wave transducer is connected to said demodulating means said third electro-acoustic wave transducer is connected in parallel and in phase with said second electro-acoustic wave transducer.
 4. A stereophonic broadcasting receiving system as claimed in claim 1 which includes means for changing the ratio of the amplitudes of the sum signal to the difference signal. 